Piezoelectric actuator

Abstract

A piezoelectric actuator disposed to face a plurality of pressure chambers, the piezoelectric actuator including a plurality of piezoelectric layers and a plurality of electrode layers which are alternately stacked on each other; and a plurality of active portions which are provided in the piezoelectric layers to be aligned with the pressure chambers, respectively, and are defined between at least one pair of electrode layers that are opposed to each other in a direction of stacking of the piezoelectric layers and the electrode layers, the active portions being deformed when an electric voltage is applied to the electrode layers, the electrode layers including (a) at least one individual-electrode layer including a plurality of individual electrodes which are aligned with the pressure chambers, respectively, (b) at least one first common-electrode layer including a plurality of first common electrodes which are maintained at a common electric potential and are aligned with the pressure chambers, respectively, and (c) at least one second common-electrode layer including at least one second common electrode which is maintained at the common electric potential and is opposed commonly to the plurality of pressure chambers.

1. A piezoelectric actuator disposed to face a plurality of pressure chambers, the piezoelectric actuator comprising:
 a plurality of piezoelectric layers and a plurality of electrode layers which are alternately stacked on each other; and 
 a plurality of active portions which are provided in the piezoelectric layers to be aligned with the pressure chambers, respectively, and are defined between at least one pair of electrode layers that are opposed to each other in a direction of stacking of the piezoelectric layers and the electrode layers, the active portions being deformed when an electric voltage is applied to the electrode layers, the electrode layers comprising (a) at least one individual-electrode layer including a plurality of individual electrodes which are aligned with the pressure chambers, respectively, (b) at least one first common-electrode layer including a plurality of first common electrodes which are maintained at a common electric potential and are aligned with the pressure chambers, respectively, and (c) at least one second common-electrode layer including at least one second common electrode which is maintained at the common electric potential and is opposed commonly to the plurality of pressure chambers, 
 wherein said at least one second common-electrode layer is provided by at least one of opposite outermost layers of the electrode layers. 
 
     
     
       2. The piezoelectric actuator according to  claim 1 , wherein the plurality of active portions in the piezoelectric layers include:
 a plurality of first active portions which are aligned with the pressure chambers, respectively, and are sandwiched by the first common electrodes of said at least one first common-electrode layer and the individual electrodes of said at least one individual-electrode layer; and 
 a plurality of second active portions which are aligned with the pressure chambers, respectively, and are sandwiched by said at least one second common electrode and the individual electrodes of said at least one individual-electrode layer, 
 each of the first active portions being deformed together with a corresponding one of the second active portions when an electric voltage is applied to a corresponding one of the individual electrodes, the first common electrodes, and said at least one second common electrode. 
 
     
     
       3. The piezoelectric actuator according to  claim 1 , wherein said at least one second common-electrode layer is provided on at least one of respective outer surfaces of opposite outermost layers of the piezoelectric layers each of which has the active portions, such that said at least one second common electrode is opposed commonly to the plurality of pressure chambers. 
     
     
       4. The piezoelectric actuator according to  claim 3 , wherein the electrode layers comprise (c) two said second common-electrode layers each of which includes at least one second common electrode, which are maintained at the common electric potential, and which are provided on the respective outer surfaces of the opposite outermost layers of the piezoelectric layers, such that said at least one second common electrode of each of the two second common-electrode layers is opposed commonly to the plurality of pressure chambers. 
     
     
       5. The piezoelectric actuator according to  claim 4 , wherein the electrode layers comprise (a) a plurality of said individual-electrode layers each of which includes a plurality of individual electrodes which are aligned with the pressure chambers, respectively, and (b) a plurality of said first common-electrode layers each of which includes a plurality of first common electrodes which are maintained at the common electric potential and are aligned with the pressure chambers, respectively, and wherein the individual-electrode layers and the first common-electrode layers are each stacked on a corresponding one of the piezoelectric layers, and are provided alternately between the two second common-electrode layers. 
     
     
       6. The piezoelectric actuator according to  claim 1 , wherein each of the pressure chambers has an elongate shape, each of the individual electrodes has an elongate shape overlapping a corresponding one of the pressure chambers, and each of the first common electrodes has an elongate shape overlapping a corresponding one of the individual electrodes and a corresponding one of the pressure chambers. 
     
     
       7. The piezoelectric actuator according to  claim 6 , wherein said each pressure chamber has a first width, and said each individual electrode has a second width that is not greater than the first width. 
     
     
       8. The piezoelectric actuator according to  claim 7 , wherein said each first common electrode has a third width that is greater than the second width. 
     
     
       9. The piezoelectric actuator according to  claim 8 , wherein the third width is not greater than the first width. 
     
     
       10. The piezoelectric actuator according to  claim 1 , wherein the piezoelectric actuator is assembled into an ink jet printer head having the pressure chambers, and wherein the active portions are aligned with the pressure chambers of the ink jet printer head, respectively. 
     
     
       11. The piezoelectric actuator according to  claim 1 , wherein the first common electrodes are formed of silver-palladium alloy. 
     
     
       12. The piezoelectric actuator according to  claim 1 , wherein said at least one first common-electrode layer and said at least one second common-electrode layer cooperate with each other to sandwich, therebetween, at least two piezoelectric layers of the plurality of piezoelectric layers, and wherein each of said at least two piezoelectric layers has at least one through-hole which is formed through a thickness thereof and is provided with an electrically conductive material such that said at least one first common-electrode layer and said at least one second common-electrode layer are electrically connected to each other. 
     
     
       13. An ink jet printer head, comprising:
 a cavity unit having a plurality of ink ejection nozzles and a plurality of ink chambers in each of which an ink is accommodated and each of which communicates with a corresponding one of the ink ejection nozzles; and 
 a piezoelectric actuator which changes a pressure of the ink accommodated in said each ink chamber, so as to eject a droplet of the ink from the corresponding ink ejection nozzle the piezoelectric actuator including 
 a plurality of piezoelectric layers and a plurality of electrode layers which are alternately stacked on each other, and 
 plurality of active portions which are provided in the piezoelectric layers to be aligned with the ink chambers, respectively, and are defined between at least one pair of electrode layers that are opposed to each other in a direction of stacking of the piezoelectric layers and the electrode layers, the active portions being deformed when an electric voltage is applied to the electrode layers, 
 the electrode layers comprising (a) at least one individual-electrode layer including a plurality of individual electrodes which are aligned with the ink chambers, respectively, (b) at least one first common-electrode layer including a plurality of first common electrodes which are maintained at a common electric potential and are aligned with the ink chambers, respectively, and (c) at least one second common-electrode layer including at least one second common electrode which is maintained at the common electric potential and is opposed commonly to the plurality of ink chambers, 
 wherein said at least one second common-electrode layer is provided by at least one of opposite outermost layers of the electrode layers. 
 
     
     
       14. The ink jet printer head according to  claim 13 , wherein the plurality of active portions in the piezoelectric layers include:
 a plurality of first active portions which are aligned with the ink chambers, respectively, and are sandwiched by the first common electrodes of said at least one first common-electrode layer and the individual electrodes of said at least one individual-electrode layer; and 
 a plurality of second active portions which are aligned with the ink chambers, respectively, and are sandwiched by said at least one second common electrode and the individual electrodes of said at least one individual-electrode layer, 
 each of the first active portions being deformed together with a corresponding one of the second active portions when an electric voltage is applied to a corresponding one of the individual electrodes, the first common electrodes, and said at least one second common electrode. 
 
     
     
       15. The ink jet printer head according to  claim 13 , wherein said at least one second common-electrode layer is provided on at least one of respective outer surfaces of opposite outermost layers of the piezoelectric layers each of which has the active portions, such that said at least one second common electrode is opposed commonly to the plurality of ink chambers. 
     
     
       16. The ink jet printer head according to  claim 15 , wherein the electrode layers comprises (c) two said second common-electrode layers each of which includes at least one second common electrode, which are maintained at the common electric potential, and which are provided on the respective outer surfaces of the opposite outermost layers of the piezoelectric layers, such that said at least one second common electrode of each of the two second common-electrode layers is opposed commonly to the plurality of ink chambers. 
     
     
       17. The ink jet printer head according to  claim 15 , wherein the piezoelectric actuator is fixed to the cavity unit, such that said one of the respective outer surfaces of the opposite outermost layers of the piezoelectric layers, on which the second common-electrode layer is provided, is nearer to the ink chambers of the cavity unit than the other outer surface. 
     
     
       18. The ink jet printer head according to  claim 13 , wherein the first common electrodes are formed of silver-palladium alloy. 
     
     
       19. A piezoelectric actuator disposed to face a plurality of pressure chambers, the piezoelectric actuator comprising:
 a plurality of piezoelectric layers and a plurality of electrode layers which are alternately stacked on each other; and 
 a plurality of active portions which are provided in the piezoelectric layers to be aligned with the pressure chambers, respectively, and are defined between at least one pair of electrode layers that are opposed to each other in a direction of stacking of the piezoelectric layers and the electrode layers, the active portions being deformed when an electric voltage is applied to the electrode layers, 
 wherein the electrode layers comprise (a) at least one individual-electrode layer including a plurality of individual electrodes which are aligned with the pressure chambers, respectively, (b) at least one first common-electrode layer including a plurality of first common electrodes which are maintained at a common electric potential and are aligned with the pressure chambers, respectively, and (c) at least one second common-electrode layer including at least one second common electrode which is maintained at the common electric potential and is opposed commonly to the plurality of pressure chambers, 
 wherein each of the pressure chambers has an elongate shape, each of the individual electrodes has an elongate shape overlapping a corresponding one-of the pressure chambers, and each of the first common electrodes has an elongate shape overlapping a corresponding one of the individual electrodes and a corresponding one of the pressure chambers, and 
 wherein said each first common electrode has a width that is greater than a width of said each individual electrode. 
 
     
     
       20. The piezoelectric actuator according to  claim 19 , wherein the width of said each individual electrode is not greater than a width of said each pressure chamber. 
     
     
       21. The piezoelectric actuator according to  claim 19 , wherein the width of said each first common electrode is not greater than a width of said each pressure chamber.